The present invention relates to an ink cartridge which supplies ink at an appropriate negative pressure to a recording head which ejects ink droplets in response to print signals applied thereto.
The ink jet recording device is usually constructed such that an ink jet recording head for ejecting ink droplets in response to print signals is mounted on a carriage which is reciprocatively moved in the width direction of a recording sheet, and ink is supplied from an ink tank, located outside, to the recording head. In the recording device of the small type, an ink storage container, such as an ink tank, is detachably attached to the carriage to secure easy handling.
In general, the ink storage container contains a porous member in order to prevent ink from leaking out of the recording head. The porous member is impregnated with ink, whereby the ink is held by a capillary force.
Improvement of print quality and printing speed is demanded in the market. Thus, there is a tendency that the number of nozzle openings of the recording head is increased, and an amount of ink consumed per unit time is increased.
To meet this tendency, it is necessary to increase the amount of ink stored in the ink storage container. As a result, the volume of the porous member is increased. However, in view of holding ink by the capillary force of the porous member, a height, or a water head, is limited in increase, and consequently, the bottom area need to be increased. This results in the increase of the carriage size, and thus the recording device.
There is an approach in which the ink holding capability is increased by using a porous member small in average pore diameter. However, this approach increases fluid resistance against the ink flow, causing difficulty not only in stably supplying ink correspondingly to the amount of ink consumed by the recording head, but also in reliably supplying, to the recording head, ink in a region distanced from an ink supply port. As a result, the ink contained in the ink container is not consumed completely and left therein as waste ink.
To solve the problem, such an ink storage container is proposed, as disclosed in JP-A-8-174860, that an ink storage chamber is located in the upper part, and a normally closed-membrane (film) valve is provided between the ink storage chamber and the ink supply port so that the valve is opened by a negative pressure caused with the ink consumption by the recording head.
Since the membrane valve can prevent the leakage of ink, the amount of stored ink can be increased. However, a pressure corresponding to the ink amount acts on the membrane valve since the ink storage chamber is located in the upper part. Therefore, to increase the amount of the stored ink without increasing the bottom area, the negative pressure for opening the membrane valve must be increased. As a result, the print quality is degraded at a time point that the remaining ink amount is small, that is, the water head pressure of the ink is decreased below a predetermined level. On the other hand, if the print quality must be ensured, the remaining ink amount is increased.
Further, if printing is continued while disregarding the print quality in order to decrease the waste ink, an excess negative pressure required to open the membrane valve acts on the recording head to destroy the meniscuses at the nozzles of the recording head, making the printing impossible.